One of the limited-diffraction beams, the Bessel beam, was first studied theoretically by Stratton [1] and then experimentally by Durnin et al [2]-[3]. In 1991, new families of limited-diffraction beams such as X waves were discovered [4]-[8]. X waves are multiple-frequency waves and have the same phase and group velocity. Theoretically, limited-diffraction beams can propagate to an infinite distance without spreading. In practice, when these beams are produced with finite aperture and energy, they have a large depth of field. Because of this property, limited-diffraction beams have potential applications in medical imaging [9]-[11], tissue identification [12], nondestructive evaluation (NDE) of materials [13], Doppler blood flow measurement [14]-[15], fast computation of fields of 2D array transducers [16], optical communications [17], and other optics [18] and physics related areas [19]. Recently, X waves have been studied in nonlinear optics [20] and reported in the “Search and Discovery” column of [21].
Based on the studies of limited-diffraction beams [22]-[23], a two-dimensional (2D) and three-dimensional (3D) high frame rate (HFR) imaging method was developed in 1997 [24]-[26] with its importance reported in [27].
Recently, the present inventor herein discovered a system for extended high frame rate imaging using limited diffraction beams, which is disclosed in the co-pending PCT patent application PST/US06/033751 filed Aug. 29, 2006, which is expressly incorporated herein by reference, and which was later the subject of several publications. [28]-[32].
The extended HFR imaging method increases image resolution and field of view [37] as compared to the conventional delay-and-sum (D&S) methods with a fixed transmission focus [38] and dynamically focused reception. As more and more limited-diffraction array beams of different parameters or plane waves steered at different angles are transmitted (lower image frame rate), the image quality increases. The trade-off between the image quality and frame rate is useful for imaging of organs that do not move fast, such as the liver and kidney.
Although the extended high-frame rate imaging method has many advantages, an imaging system to implement this method still has many challenges, such as: i) the imaging system is complicated and requires a large amount of power to operate and thus is difficult to be integrated to a transducer probe that a physician can hold to move freely around a patient; ii) the amount of data acquired by an array transducer, especially, an array of a large number of elements such as two-dimensional arrays, is huge and thus would be difficult to be transferred to a separate imaging system through fewer cables; iii) there would be too many cables to send transmit signals to individual transducer elements to produce ultrasound for an array with a large number elements; and iv) the image reconstruction process is complicated and requires many circuits.
Therefore, there is a compelling and crucial need in the art to simplify imaging systems for fast multi-dimensional ultrasound imaging that is made and operated at low cost.